1. Field of the Invention
The present invention relates to a key sheet used for an operating part of various kinds of equipment such as a mobile-phone, a PDA, a car navigation system, and a car audio system, and a manufacturing method thereof.
2. Description of the Related Art
In a mobile-phone (1) shown in FIG. 15, a key sheet (11) shown in FIG. 16 is used. The key sheet (11) is a base sheet (12) made of silicone gum on which a plurality of, total 21 pieces of, key tops (13) made of a hard resin is fixed by dropping an UV adhesive or the like. When a key top (13) is pushed, the base sheet (12) is bend, thereby a contact electrode on a circuit board (not shown) located on the bottom surface of the key sheet is pushed to be a state of switch input, and when pushing is removed, the key top (13) is returned to its initial position by the restoring force of the base sheet (12), and the state of switch input is released.
Meanwhile, recently, as shown in FIG. 17, a mobile-phone (2) is also used, where an operating opening (2a) with no partitioning crosspiece (1b) (FIG. 15) between key tops (23) is opened, and from the opening, a key sheet (21) shown in FIG. 18, is exposed, where key tops (23) are arranged with a narrower gap between key tops (23). Since the mobile-phone (2) has no partitioning crosspiece (1b) (FIG. 15), in the key sheet (21), it is required to support the entire mobile-phone (2) only by the surrounding of the key sheet (21). Consequently, the base (22) is not made of rubber-like elastic body (22a) only, rather, as shown in FIG. 19, it has a construction where reinforcement (22b) such as hard resin and fiber reinforcement is provided among the rubber-like elastic body (22a). Such a key sheet is described, for example, in Japanese unexamined Patent Application Publication No. 2005-63975.
However, since it is noticeable of the change of design with respect to the mobile-phone, as a result of consideration for a key sheet with more fresh design, as an improved version of the above-mentioned key sheets (11 and 21), the inventors of the present invention devised a key sheet that is designed to have a frame corresponding to the partitioning crosspiece for partitioning each key top, and where a plurality of key tops and also the frame itself are exposed from an operating opening with no partitioning crosspiece of the mobile-phone. However, it was known that the improved version key sheet cannot be manufactured by modifying the structure of the conventional key sheets (11, 21), or by means of its manufacturing method.
In order to manufacture the conventional key sheets (11 and 21), a liquid adhesive such as an UV curing adhesive has been coated on the bottom surfaces of resin key tops (13 and 23), and the key tops (13 and 23) have been adhered to the base sheets (12 and 22). In this method, in order to prevent the adhesive from protruding from the key tops (13 and 23), only the center parts of the bottom surfaces of the key tops (13 and 23) have been coated with the adhesive. Consequently, the bottom surfaces of the key tops (13 and 23) have been coated with the adhesive not entirely, and gaps have occurred between the key tops (13 and 23) and the base sheets (12 and 22). It is the presence of the gaps that causes a problem of coming off of key tops.
In other words, as for the gaps, in the conventional key sheet (11), since a flange is formed around the key tops (13), and the mobile-phone (1) to be mounted has the partitioning crosspiece (1b), the coming off of the key tops (13) is substantially acceptable. However, since, in the key sheet (21) where key tops (23) are arranged with a narrower gap between key tops (23 and 23), the housing of the equipment has no partitioning crosspiece, and also the flange is not formed, there is a possibility for a nail for pushing operation to enter the gaps between the key tops (23) and the base sheet fixing the key tops (23), resulting in the possibility that the key tops (23) come off from the key sheet (21).
Moreover, in the improved version key sheet where gaps between key tops are wider, and the frame is exposed, since the possibility for a nail to enter the gaps between the key tops and the base sheet becomes higher than that of the key sheet (21) where key tops (23) are arranged with narrower gaps, the coming off of the key tops causes larger problems.